U.S. patent application number 11/018406 was filed with the patent office on 2006-06-22 for wellbore tool with disintegratable components.
Invention is credited to Michael McKeachnie, W. John McKeachnie, Rocky A. Turley, Scott Williamson.
Application Number | 20060131031 11/018406 |
Document ID | / |
Family ID | 36594252 |
Filed Date | 2006-06-22 |
United States Patent
Application |
20060131031 |
Kind Code |
A1 |
McKeachnie; W. John ; et
al. |
June 22, 2006 |
Wellbore tool with disintegratable components
Abstract
The present invention generally provides a pressure isolation
plug for managing a wellbore with multiple zones. The pressure
isolation plug generally includes a body with a bore extending
therethrough, a first disintegratable ball sized and positioned to
restrict upward fluid flow through the bore, wherein the
disintegratable ball disintegrates when exposed to wellbore
conditions for a first amount of time. The plug also includes a
second ball sized and positioned to restrict downward fluid flow
through the bore.
Inventors: |
McKeachnie; W. John;
(Vernal, UT) ; McKeachnie; Michael; (Vernal,
UT) ; Williamson; Scott; (Castle Rock, CO) ;
Turley; Rocky A.; (Houston, TX) |
Correspondence
Address: |
PATTERSON & SHERIDAN, L.L.P.
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
36594252 |
Appl. No.: |
11/018406 |
Filed: |
December 21, 2004 |
Current U.S.
Class: |
166/376 ;
166/317; 166/382; 166/387 |
Current CPC
Class: |
E21B 33/134 20130101;
E21B 33/1294 20130101 |
Class at
Publication: |
166/376 ;
166/382; 166/387; 166/317 |
International
Class: |
E21B 29/00 20060101
E21B029/00; E21B 23/00 20060101 E21B023/00 |
Claims
1. A method of operating a downhole tool, comprising: providing the
tool having at least one disintegratable ball seatable in the toot
to block a flow of fluid therethrough in at least one direction;
causing the ball to seat and block the fluid; permitting the ball
to disintegrate after a predetermined time period, thereby
reopening the tool to the flow of fluid.
2. The method of claim 1, further comprising providing a
disintegratable annular ball seat in the tool.
3. The method of claim 1, further comprising providing a second
ball seatable in the tool to block the flow of fluid therethrough
in a second direction.
4. The method of claim 3, wherein the second ball is
disintegratable.
5. A method of isolating one section of a wellbore from another,
comprising: providing a pressure isolation plug; utilizing a first
disintegratable ball to restrict upward flow and isolate pressure
below the pressure isolation plug; utilizing a second
disintegratable ball to restrict downward flow and isolate pressure
above the pressure isolation plug; exposing the first
disintegratable ball and the second disintegratable ball to
wellbore conditions for a first amount of time, causing the first
disintegratable ball to disintegrate; and allowing upward flow to
resume through the pressure isolation plug.
6. The method of claim 5, further comprising: exposing the second
disintegratable ball to wellbore conditions for a second amount of
time, causing the second disintegratable ball to disintegrate.
7. The method of claim 5, the wellbore conditions comprise water
and heat.
8. A method of isolating one section of a wellbore from another,
comprising: providing a pressure isolation plug; utilizing a
disintegratable ball to restrict upward fluid flow and isolate
pressure below the pressure isolation plug; exposing the ball to
wellbore conditions including water and heat, thereby allowing the
ball to disintegrate; and allowing upward fluid flow to resume
through the pressure isolation plug.
9. The method of claim 8, wherein the wellbore conditions comprise
water and heat.
10. An apparatus for isolating one section of a wellbore from
another, comprising: a body with a bore extending therethrough; and
a disintegratable ball sized to fluid flow through the bore,
wherein the disintegratable ball disintegrates when exposed to
wellbore conditions for a given amount of time.
11. The apparatus of claim 10, further comprising a disintegratable
annular ball seat.
12. An apparatus for isolating one section of a wellbore from
another, comprising: a body with a bore extending therethrough; a
first disintegratable ball sized and positioned to restrict upward
fluid flow through the bore, wherein the disintegratable ball
disintegrates when exposed to wellbore conditions for a first
amount of time; and a second ball sized and positioned to restrict
downward fluid flow through the bore.
13. The apparatus of claim 12, wherein the second ball is
disintegratable and is configured to disintegrate when exposed to
wellbore conditions for a second amount of time.
14. The apparatus of claim 12, further comprising a disintegratable
annular ball seat.
15. An apparatus for use in a wellbore comprising: a body; a slip
assembly for fixing the body at a predetermined location in a
wellbore, F the slip assembly arranged to frictionally contact the
wellbore walls; whereby at least one portion of the slip assembly
is made of a disintegratable material constructed and arranged to
lose its structural integrity after a predetermined amount of
time.
16. The apparatus of claim 15, wherein the apparatus is a
packer.
17. The apparatus of claim 15, wherein the apparatus is a bridge
plug.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments of the present invention are generally related
to oil and gas drilling. More particularly, embodiments of the
present invention pertain to pressure isolation plugs that utilize
disintegratable components to provide functionality typically
offered by frac plugs and bridge plugs.
[0003] 2. Description of the Related Art
[0004] An oil or gas well includes a wellbore extending into a well
to some depth below the surface. Typically, the wellbore is lined
with a string of tubulars, such as casing, to strengthen the walls
of the borehole. To further reinforce the walls of the borehole,
the annular area formed between the casing and the borehole is
typically filled with cement to permanently set the casing in the
wellbore. The casing is then perforated to allow production fluid
to enter the wellbore from the surrounding formation and be
retrieved at the surface of the well.
[0005] Downhole tools with sealing elements are placed within the
wellbore to isolate the production fluid or to manage production
fluid flow into and out of the well. Examples of such tools are
frac plugs and bridge plugs. Frac plugs (also known as fracturing
plugs) are pressure isolation plugs that are used to sustain
pressure due to flow of fluid that is pumped down from the surface.
As their name implies, frac plugs are used to facilitate fracturing
jobs. Fracturing, or "fracing", involves the application of
hydraulic pressure from the surface to the reservoir formation to
create fractures through which oil or gas may move to the well
bore. Bridge plugs are also pressure isolation devices, but unlike
frac plugs, they are configured to sustain pressure from below the
plug. In other words, bridge plugs are used to prevent the upward
flow of production fluid and to shut in the well at the plug.
Bridge plugs are often run and set in the wellbore to isolate a
lower zone while an upper section is being tested or cemented.
[0006] Frac plugs and bridge plugs that are available in the
marketplace typically comprise components constructed of steel,
cast iron, aluminum, or other alloyed metals. Additionally, frac
plugs and bridge plugs include a malleable, synthetic element
system, which typically includes a composite or synthetic rubber
material which seals off an annulus within the wellbore to restrict
the passage of fluids and isolate pressure. When installed, the
element system is compressed, thereby expanding radially outward
from the tool to sealingly engage a surrounding tubular. Typically,
a frac plug or bridge plug is placed within the wellbore to isolate
upper and lower sections of production zones. By creating a
pressure seal in the wellbore, bridge plugs and frac-plugs isolate
pressurized fluids or solids. Operators are taking advantage of
functionality provided by pressure isolation devices such as frac
plugs and bridge plugs to perform a variety of operations (e.g.,
cementation, liner maintenance, casing fracs, etc.) on multiple
zones in the same wellbore--such operations require temporary zonal
isolation of the respective zones.
[0007] For example, for a particular wellbore with multiple (i.e.,
two or more) zones, operators may desire to perform operations that
include: fracing the lowest zone; plugging it with a bridge plug
and then fracing the zone above it; and then repeating the previous
steps until each remaining zone is fraced and isolated. With
regards to frac jobs, it is often desirable to flow the frac jobs
from all the zones back to the surface. This is not possible,
however, until the previously set bridge plugs are removed. Removal
of conventional pressure isolation plugs (either retrieving them or
milling them up) usually requires well intervention services
utilizing either threaded or continuous tubing, which is time
consuming, costly and adds a potential risk of wellbore damage.
[0008] Certain pressure isolation plugs developed that hold
pressure differentials from above while permitting flow from below.
However, too much flow from below will damage the ball and seat
over time and the plug will not hold pressure when applied from
above.
[0009] There is a need for a pressure isolation device that
temporarily provides the pressure isolation of a frac plug or
bridge plug, and then allows unrestricted flow through the
wellbore. One approach is to use disintegratable materials that are
water-soluble. As used herein, the term "disintegratable" does not
necessarily refer to a material's ability to disappear. Rather,
"disintegratable" generally refers to a material's ability to lose
its structural integrity. Stated another way, a disintegratable
material is capable of breaking apart, but it does not need to
disappear. It should be noted that use of disintegratable materials
to provide temporary sealing and pressure isolation in wellbores is
known in the art. For some operations, disintegratable balls
constructed of a water-soluble composite material are introduced
into a wellbore comprising previously created perforations. The
disintegratable balls are used to temporarily plug up the
perforations so that the formation adjacent to the perforations is
isolated from effects of the impending operations. The material
from which the balls are constructed is configured to disintegrate
in water at a particular rate. By controlling the amount of
exposure the balls have to wellbore conditions (e.g., water and
heat), it is possible to plug the perforations in the above manner
for a predetermined amount of time.
[0010] It would be advantageous to configure a pressure isolation
device or system to utilize these disintegratable materials to
temporarily provide the pressure isolation of a frac plug or bridge
plug, and then provide unrestricted flow. This would save a
considerable amount of time and expense. Therefore, there is a need
for an isolation device or system that is conducive to providing
zonal pressure isolation for performing operations on a wellbore
with multiple production zones. There is a further need for the
isolation device or system to maintain differential pressure from
above and below for a predetermined amount of time.
SUMMARY OF THE INVENTION
[0011] One embodiment of the present invention provides a method of
operating a downhole tool. The method generally includes providing
the tool having at least one disintegratable ball seatable in the
tool to block a flow of fluid therethrough in at least one
direction, causing the ball to seat and block the fluid, and
permitting the ball to disintegrate after a predetermined time
period, thereby reopening the tool to the flow of fluid.
[0012] Another embodiment of the present invention provides a
method of managing a wellbore with multiple zones. The method
generally includes providing a pressure isolation plug, utilizing a
first disintegratable ball to restrict upward flow and isolate
pressure below the pressure isolation plug, utilizing a second
disintegratable ball to restrict downward flow and isolate pressure
above the pressure isolation plug, exposing the first
disintegratable ball and the second disintegratable ball to
wellbore conditions for a first amount of time, causing the first
disintegratable ball to disintegrate, and allowing upward flow to
resume through the pressure isolation plug
[0013] Another embodiment of the present invention provides a
method of managing a wellbore with multiple zones. The method
generally includes providing a pressure isolation plug, utilizing a
disintegratable ball to restrict upward fluid flow and isolate
pressure below the pressure isolation plug, exposing the ball to
wellbore conditions including water and heat, thereby allowing the
ball to disintegrate, and allowing upward fluid flow to resume
through the pressure isolation plug.
[0014] Another embodiment of the present invention provides an
apparatus for managing a wellbore with multiple zones. The
apparatus generally includes a body with a bore extending
therethrough, and a disintegratable ball sized to fluid flow
through the bore, wherein the disintegratable ball disintegrates
when exposed to wellbore conditions for a given amount of time.
[0015] Another embodiment of the present invention provides an
apparatus for managing a wellbore with multiple zones. The
apparatus generally includes a body with a bore extending
therethrough, a first disintegratable ball sized and positioned to
restrict upward fluid flow through the bore, wherein the
disintegratable ball disintegrates when exposed to wellbore
conditions for a first amount of time. The apparatus also includes
a second ball sized and positioned to restrict downward fluid flow
through the bore.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0017] FIG. 1 is a cross-sectional view of a wellbore illustrating
a string of tubulars having a pressure isolation plug in accordance
with one embodiment of the present invention.
[0018] FIG. 2 is a detailed cross-sectional view of a pressure
isolation plug in accordance with one embodiment of the present
invention.
[0019] FIG. 3 is another detailed cross-sectional view of the
pressure isolation plug shown in FIG. 2.
[0020] FIG. 4 is a detailed cross-sectional view of a pressure
isolation plug in accordance with an alternative embodiment of the
present invention.
[0021] FIG. 5 is a detailed cross-sectional view of a pressure
isolation plug in accordance with yet another embodiment of the
present invention.
DETAILED DESCRIPTION
[0022] The apparatus and methods of the present invention include
subsurface pressure isolation plugs for use in wellbores.
Embodiments of the present invention provide pressure isolation
plugs that utilize disintegratable components to provide
functionality typically offered by frac plugs and bridge plugs. The
plugs are configured to provide such functionality for a
predetermined amount of time. It should be noted that while
utilizing pressure isolation plugs of the present invention as frac
plugs and bridge plugs is described herein, they may also be used
as other types of pressure isolation plugs.
[0023] FIG. 1 is a cross-sectional view of a wellbore 10
illustrating a string of tubulars 11 having an pressure isolation
plug 200 in accordance with one embodiment of the present
invention. The string of tubulars may be a string of casing or
production tubing extending into the wellbore from the surface. As
will be described in detail below, the pressure isolation plug 200
may be configured to used as a frac plug, bridge plug or both.
Accordingly, the pressure isolation plug 200, also referred to
herein as simply "plug" 200, may isolate pressure from above, below
or both. For instance, as seen in FIG. 1, if the plug is configured
to function as a frac plug, it isolates pressure from above and
facilitates the fracing of the formation 12 adjacent to
perforations 13. If the plug 200 is configured to function as a
bridge plug, production fluid from formation 14 entering the
wellbore 10 from the corresponding perforations 15 is restricted
from flowing to the surface.
[0024] The pressure isolation plug according to embodiments of the
present invention may be used as frac plugs and bridge plugs by
utilizing disintegratable components, such as balls, used to stop
flow through a bore of the plug 200. The balls can be constructed
of a material that is disintegratable in a predetermined amount of
time when exposed to particular wellbore conditions. The
disintegratable components and the methods in which they are used
are described in more detail with reference to FIGS. 2, 3 and
4.
[0025] FIG. 2 is a detailed cross sectional view of a pressure
isolation plug 200. The plug 200 generally includes a mandrel 201,
a packing element 202 used to seal an annular area between the plug
200 and an inner wall of the tubular string 11 therearound (not
shown), and one or more slips 203A and 203B. The packing element
202 is disposed between upper and lower retainers 205A and 205B. In
operation, axial forces are applied to the upper slip 203A while
the mandrel 201 and the lower slip 203B are held in a fixed
position. As the upper slip 203A moves down in relation to the
mandrel 201 and lower slip 203B, the packing element 202 is
actuated and the upper slip 203A and lower slip 203B are driven up
cones 204A and 204B, respectively. The movement of the cones and
the slips axially compress and radially expand the packing element
202 thereby forcing the sealing portion radially outward from the
plug 200 to contact the inner surface of the tubular string 11. In
this manner, the compressed packing element 202 provides a fluid
seal to prevent movement of fluids across the plug 200 via the
annular gap between the plug 200 and the interior of the tubular
string 11, thereby facilitating pressure isolation.
[0026] Application of the axial forces that are required to set the
plug 200 in the manner described above may be provided by a variety
of available setting tools well known in the art. The selection of
a setting tool may depend on the selected conveyance means, such as
wireline, threaded tubing or continuous tubing. For example, if the
plug 200 is run into position within the wellbore on wireline, a
wireline pressure setting tool may be used to provide the forces
necessary to urge the slips over the cones, thereby actuating the
packing element 202 and setting the plug 200 in place.
[0027] Upon being set in the desired position within the wellbore
10, a pressure isolation plug 200, configured as shown in FIG. 2,
is ready to function as a bridge plug and a frac plug. Upward flow
of fluid (presumably production fluid) causes the lower ball 208 to
seat in the lower ball seat 210, which allows the plug 200 to
restrict upward flow of fluid and isolate pressure from below. This
allows the plug 200 to provide the functionality of a conventional
bridge plug. It should be noted that in the absence of upward flow,
the lower ball 208 is retained within the plug 200 by retainer pin
211. Downward flow of fluid causes the upper ball 206 to seat in
the upper ball seat 209, thereby allowing the plug 200 to restrict
downward flow of fluid and isolate pressure from above; this allows
the plug to function as a conventional frac plug, which allows
fracturing fluid to be directed into the formation through the
perforations. Stated another way, the upper ball 206 acts as a
one-way check valve allowing fluid to flow upwards and the lower
ball 208 acts as a one-way check valve allowing fluid to flow
downwards.
[0028] As described earlier, for some wellbores with multiple
(i.e., two or more) zones, operators may desire to perform
operations that include fracing of multiple zones. Exemplary
operations for setting the plug 200 and proceeding with the frac
jobs are provided below. First, the plug 200 is run into the
wellbore via a suitable conveyance member (such as wireline,
threaded tubing or continuous tubing) and positioned in the desired
location. In a live well situation, while the plug 200 is being
lowered into position, upward flow is diverted around the plug 200
via ports 212. Next, the plug 200 is set using a setting tool as
described above. Upon being set, the annular area between the plug
200 and the surrounding tubular string 11 is plugged off and the
upward flow of production fluid is stopped as the lower ball 208
seats in the ball seat 210. Residual pressure remaining above the
plug 200 can be bled off at the surface, enabling the frac job to
begin. Downward flow of fracing fluid ensures that the upper ball
206 seats on the upper ball seat 209, thereby allowing the frac
fluid to be directed into the formation through corresponding
perforations. After a predetermined amount of time, and after the
frac operations are complete, the production fluid is allowed to
again resume flowing upward through the plug 200, towards the
surface. The upward flow is facilitated by the disintegration of
the lower ball 208 into the surrounding wellbore fluid. The above
operations can be repeated for each zone that is to be fraced.
[0029] For some embodiments the lower ball 208 is constructed of a
material that is designed to disintegrate when exposed to certain
wellbore conditions, such as temperature, water and heat pressure
and solution. The heat may be present due to the temperature
increase attributed to the natural temperature gradient of the
earth, and the water may already be present in the existing
wellbore fluids. The disintegration process completes in a
predetermined time period, which may vary from several minutes to
several weeks. Essentially all of the material will disintegrate
and be carried away by the water flowing in the wellbore. The
temperature of the water affects the rate of disintegration. The
material need not form a solution when it dissolves in the aqueous
phase, provided it disintegrates into sufficiently small particles,
i.e., a colloid, that can be removed by the fluid as it circulates
in the well. The disintegratable material is preferably a water
soluble, synthetic polymer composition including a polyvinyl,
alcohol plasticizer and mineral filler. Disintegratable material is
available from Oil States Industries of Arlington, Tex., U.S.A.
[0030] Referring now to FIG. 3, which illustrates the plug 200 of
FIG. 2 after the lower ball 208 has disintegrated. The upper ball
206 remains intact but still allows the production fluid to flow to
the surface--the upward flow of fluid disengages the upper ball 206
from the upper ball seat 209. A retainer pin 207 is provided to
constrain the upward movement of the ball 206. Essentially, FIG. 3
illustrates the plug 200 providing the functionality of a
conventional frac plug. During a frac job, downward flow of fluid
would cause the upper ball 206 to seat and the plug 200 would allow
fracturing fluid to be directed into the formation above the plug
200 via the corresponding perforations.
[0031] The presence of the upper ball 206 ensures that if another
frac operation is required, downward flow of fluid will again seat
the upper ball 206 and allow the frac job to commence. With regard
to the upper ball 206, if it is desired that the ball persist
indefinitely (i.e., facilitate future frac jobs), the upper ball
206 may be constructed of a material that does not disintegrate.
Such materials are well known in the art. However, if the ability
to perform future frac jobs using the plug 200 is not desired, both
the lower ball and the upper ball may be constructed of a
disintegratable material.
[0032] Accordingly, for some embodiments, the upper ball 206 is
also constructed of a disintegratable material. There are several
reasons for providing a disintegratable upper ball 206, including:
it is no longer necessary to have the ability to frac the formation
above the plug; disintegration of the ball yields an increase in
the flow capacity through the plug 200. It should be noted that if
the upper ball 206 is disintegratable too, it would have to
disintegrate at a different rate from the lower ball 208 in order
for the plug 200 to provide the functionality described above. The
upper and lower balls would be constructed of materials that
disintegrate at different rates.
[0033] While the pressure isolation plug of FIG. 2 has the
capability to sustain pressure from both directions, other
embodiments may be configured for sustaining pressure from a single
direction. In other words, the plug could be configured to function
as a particular type of plug, such as a frac plug or a bridge plug.
FIGS. 4 and 5 illustrate embodiments of the invention that only
function as frac plugs. Both embodiments are configured to isolate
pressure only from above; accordingly, each is provided with only
one ball. The disintegratable balls included with each embodiment
may be constructed of a suitable water soluble material so that
after a predetermined amount of time (presumably after the fracing
is done), the balls will disintegrate and provide an unobstructed
flow path through the plug for production fluid going towards the
surface. As stated earlier, these types of plugs are advantageous
because they allow for frac jobs to be performed, but also allow
unrestricted flow after a predetermined amount of time, without the
need of additional operations to manipulate or remove the plug from
the wellbore.
[0034] With regards to the embodiments shown in FIGS. 4 and 5, the
packing element, retainers, cones and slips shown in each figure
are identical in form and function to those described with
reference to FIG. 2. Therefore, for purposes of brevity they are
not described again. As can be seen, the primary differences are
the number of disintegratable balls (these embodiments only have
one) and the profile of the bore of the respective mandrels.
[0035] With reference to FIG. 4, plug 400 comprises a mandrel 401
with a straight bore 410 that extends therethrough. With downward
flow (i.e., pressure from above), the frac ball 406 lands on a seat
409 and isolates the remainder of the wellbore below the plug 400
from the fluid flow and pressure above the plug 400. As with FIG.
2, during upward flow, the ball 406 is raised off the seat and is
constrained by retainer pin 407. While this embodiment keeps the
ball 406 secure within the body of the tool, the flow area for
production fluid is limited to the annular area of the bore of the
mandrel 401 minus the cross-sectional area of the ball 406.
[0036] The plug 500 illustrated in FIG. 5 provides more flow area
for the upward moving production fluid, which yields higher flow
capacity than the plug described with reference to FIG. 4. This
configuration of the plug (shown in FIG. 5) provides a larger flow
area because the ball 506 can be urged upwards and away from the
ball seat 509 by the upward flow of the production fluid. In fact,
the ball 506 is carried far enough upward so that it no longer
affects the upward flow of the production fluid. The resulting flow
through the plug 500 is equal to the cross-sectional area
corresponding to the internal diameter of the mandrel 501. As with
the previous embodiments, when there is downward fluid flow, such
as during a frac operation, the ball 506 again lands on the ball
seat 509 and isolates the wellbore below the plug 500 from the
fracing fluid above.
[0037] While the discussion above describes pressure isolation
plugs comprising disintegratable balls, it should be noted that in
other embodiments various other components of the plugs may be
constructed of the disintegratable material. For example, for some
embodiments, components such as cones, slips and annular ball seats
may be constructed of disintegratable material. In one aspect,
having more disintegratable components would provide the added
benefit of leaving fewer restrictions downhole. For instance, the
mandrels described with respect to the aforementioned embodiments
could include ball seats formed on an annular sleeve (rather than
the mandrel itself) constructed of a disintegratable material,
wherein the sleeve is configured to be slidably positioned inside
the mandrel. The restriction remaining in the wellbore after the
balls and the annular sleeve containing the ball seats have
disintegrated is the mandrel itself. In other words, the flow area
of the plug after the balls disintegrate is determined by the
internal diameter of the mandrel; the internal diameter of the
mandrel can be larger due to the use of the annular sleeve
containing the ball seats--resulting in a larger available flow
area.
[0038] In some embodiments, pressure isolation plugs may be
configured to function as tools other than bridge plugs and frac
plugs. Further, in order to provide the required functionality, a
variety of components including one or more balls may be
constructed of material designed to disintegrate in a predetermined
amount of time under specific conditions.
[0039] In some embodiments, the disintegratable balls described
above may be constructed of materials that will disintegrate only
when exposed to a particular chemical that is pumped down from the
surface. In other words, wellbore conditions, such as the presence
of water and heat may not be sufficient to invoke the
disintegration of the balls.
[0040] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *